One of the confounders to any study that looks at bronchopulmonary dysplasia (BPD) is the lack of a precise definition. Most neonates with BPD do not undergo lung biopsy or any physiologic test; thus, their pulmonary disease is defined clinically, on the basis of the sustained need for supplemental oxygen at 36 weeks postmenstrual age. The validity of this definition is supported by evidence that oxygen dependence at 36 weeks is predictive of long-term impairment in pulmonary function. An inherent limitation of defining BPD by the need for supplemental oxygen is that the need for oxygen is determined by individual physicians, rather than on the basis of a physiologic assessment. Published literature cites acceptable saturation ranges from 88-98%.